The 𝐝𝐢𝐠𝐞𝐬𝐭𝐢𝐯𝐞 𝐬𝐲𝐬𝐭𝐞𝐦 is made up of organs that assist in breaking down and absorbing food. It is a long, twisting tube that starts in the mouth and ends in the anus. The digestive tube wall from the mouth to the anus is made up of four main layers or tunics.

𝑻𝒖𝒏𝒊𝒄𝒂 𝒔𝒆𝒓𝒐𝒔𝒂 is the digestive tube’s outermost layer. The visceral peritoneum is a thin layer of loose connective tissue covered by mesothelium (a form of squamous epithelium that lines bodily cavities). The serosa on either side of the tube merges together to form the mesentery, which houses the vascular and neurological supplies to the digestive tract and is continuous with the hollow lining. The 𝘵𝘶𝘯𝘪𝘤𝘢 𝘢𝘥𝘷𝘦𝘯𝘵𝘪𝘵𝘪𝘢 refers to the outer layer of connective tissue that attaches the digestive tube to neighboring structures (esophagus and rectum) rather than the tunica serosa.

𝑻𝒖𝒏𝒊𝒄𝒂 𝒎𝒖𝒔𝒄𝒖𝒍𝒂𝒓𝒊𝒔 makes the digestive tube motile. This tunic is made up of two thick layers of smooth muscle. The inner layer’s muscle fibers are circular, whereas the outer layer’s are longitudinal. This combination of circular and longitudinal smooth muscle allows the tube to squeeze and drive ingesta through the lumen. The myenteric plexus lies between the inner circular and outer longitudinal layers of smooth muscle

The 𝒕𝒖𝒏𝒊𝒄𝒂 𝒔𝒖𝒃𝒎𝒖𝒄𝒐𝒔𝒂 is a loose to dense connective tissue layer containing blood and lymphatic vessels. Also in the submucosa is the submucous plexus, a vital component of the digestive tract’s neural system that controls the mucosa.

𝑻𝒖𝒏𝒊𝒄𝒂 𝒎𝒖𝒄𝒐𝒔𝒂 lines the digestive tube’s lumen. The mucosa is the most varied of the four tunics in structure and function, allowing the tube to undertake specialized digesting activities throughout its length. The epithelial cells that cover the mucosa and so directly contact the lumen are vital in this regard. The epithelial cell sheet (𝘭𝘢𝘮𝘪𝘯𝘢 𝘦𝘱𝘪𝘵𝘩𝘦𝘭𝘪𝘢𝘭𝘪𝘴) varies along the tract. In fact, the epithelium is made up of cells that secrete, absorb or produce hormones.

The 𝘭𝘢𝘮𝘪𝘯𝘢 𝘱𝘳𝘰𝘱𝘳𝘪𝘢 is a layer of loose connective tissue underneath the epithelium that supplies blood and lymphatics to the epithelium. This layer contains lymphatic nodules vital to the digestive tract’s immune system. Finally, a thin layer of smooth muscle (𝘭𝘢𝘮𝘪𝘯𝘢 𝘮𝘶𝘴𝘤𝘶𝘭𝘢𝘳𝘪𝘴 𝘮𝘶𝘤𝘰𝘴𝘢𝘦) allows the mucosa to move and fold dynamically.